KR20000071433A - Surface acoustic wave resonator, surface acoustic wave filter, duplexer, communication apparatus, and surface acoustic wave device - Google Patents

Abstract

The surface acoustic wave resonator according to the present invention comprises: a piezoelectric substrate made of langasite single crystal; And an interdigital transducer mainly composed of Al and formed on the piezoelectric substrate. Euler angles (ψ, θ, φ) defining the direction of the piezoelectric substrate are about 11 ° to 13 °, about 152 ° to 155 ° and about 37 ° ± 2 °, or equivalent to each other. The film thickness H of the interdigital transducer is between about 0.005 and 0.15 with respect to the wavelength? Of the surface acoustic wave excited on the piezoelectric substrate.

Description

Surface acoustic wave resonator, surface acoustic wave filter, duplexer, communication apparatus, and surface acoustic wave device

The present invention, the surface of the elastic wave resonator, a surface the surface acoustic wave filter, including the acoustic wave resonator, relates to a duplexer and a communication apparatus and, more particularly, Palanga site as the piezoelectric substrate (La ₃ Ga ₅ SiO ₁₄₎ using a single crystal A surface acoustic wave resonator.

Surface acoustic wave resonators are widely used in band pass filters and other components included in mobile communication devices. Such surface acoustic wave resonators and surface acoustic wave filters include interdigital transducers (IDTs) in which comb-shaped electrodes are formed on piezoelectric substrates.

Piezoelectric substrates included in the surface acoustic wave resonators and surface acoustic wave filters described above include piezoelectric single crystals such as lithium niobate (LiNbO ₃ ), lithium tantalate (LiTaO ₃ ), quartz, and lithium tetraborate (Li ₂ B ₄ O ₇ ). Can be made with

In these surface acoustic wave resonators and surface acoustic wave filters, an electromechanical coupling coefficient (K ² ) mainly representing the conversion efficiency between electrical energy and mechanical energy should be as large as possible, and group delay showing the rate of change of the frequency affected by temperature. The temperature characteristic (TCD) of time should be small.

Since the surface acoustic wave filter having a substrate made of LiNbO ₃ or LiTaO ₃ has a large K ² , the difference between the resonant frequency and the anti-resonant frequency is large and has a relatively wide bandwidth. However, in contrast, since the surface acoustic wave filter has a large TCD compared with quartz, there is a disadvantage in that the frequency variation affected by the temperature is large.

On the contrary, the surface acoustic wave filter having the substrate made of quartz has an advantage that there is little variation in frequency caused by temperature due to a very low TCD. However, such a surface acoustic wave filter has a disadvantage that since K ² is small, the difference between the resonance frequency and the anti-resonant frequency is small and the bandwidth is relatively narrow.

As a result, Li ₂ B ₄ O ₇ is used for the surface acoustic wave filter and the surface acoustic wave resonator as a material having a smaller TCD than LiNbO ₃ or LiTaO ₃ and a larger K ² than quartz. However, Li ₂ B ₄ O ₇ has a disadvantage in that it is difficult to handle because it has deliquescent properties, and further, productivity is low because the growth rate of the single crystal is slow. In addition, Li ₂ B ₄ O ₇ has a good temperature characteristic with respect to frequency. However, the bad and the temperature characteristic of the K ^2, there is a problem that as a result, the band is changed with the temperature.

Recently, La ₃ Ga ₅ SiO ₁₄ has been studied as a material for solving the above problems. The reason for this is that La ₃ Ga ₅ SiO ₁₄ is easy to handle because it has no deliquescent property, and the growth rate of the single crystal is faster than that of Li ₂ B ₄ O ₇ . In addition, La ₃ Ga ₅ SiO ₁₄ has a smaller TCD and larger K ² than quartz compared to LiNbO ₃ or LiTaO ₃ . A number of theoretical analyzes and experimental results regarding the propagation direction and the promising Euler angle and propagation direction of such a La ₃ Ga ₅ SiO ₁₄ single crystal substrate have been reported.

However, the measured results and the related data in these reports are the results of experiments using only a La ₃ Ga ₅ SiO ₁₄ single crystal substrate. As a result, TCD is optimal when the La ₃ Ga ₅ SiO ₁₄ single crystal substrate is used alone, but not optimal when other elements are added.

In order to solve the above problems, a preferred embodiment of the present invention is to improve the TCD of the surface acoustic wave resonator using La ₃ Ga ₅ SiO ₁₄ single crystal.

1 is a perspective view of a surface acoustic wave resonator illustrating a first embodiment of the present invention.

2 is a perspective view of a vertically coupled surface acoustic wave filter for explaining a second embodiment of the present invention.

3 is a perspective view of a horizontally coupled surface acoustic wave filter for explaining a third embodiment of the present invention.

4 is a block diagram of a communication device for explaining a fourth embodiment of the present invention.

5 is a characteristic diagram showing a relationship between temperature and frequency variation with respect to the Euler angle.

6 is a characteristic diagram showing the relationship between the Euler angle and the peak temperature.

7 is a characteristic diagram showing the relationship between temperature and frequency variation with respect to electrode film thickness.

8 is a characteristic diagram showing a relationship between an electrode film thickness and an Euler angle for explaining a preferred embodiment of the present invention.

* Description of the symbols for the main parts of the drawings *

1: surface acoustic wave resonator

2: piezoelectric substrate

3: interdigital transducer

3a, 3b: comb-shaped electrode

A surface acoustic wave resonator according to a preferred embodiment of the present invention includes a piezoelectric substrate made of langagasite single crystal, and an interdigital transducer including Al and formed on the piezoelectric substrate, wherein the Euler angle (ψ, θ and φ) are about 11 ° to 13 °, about 152 ° to 155 ° and about 37 ° ± 2 °, respectively, and the film thickness H of the interdigital transducer is used to determine the surface acoustic wave excited on the piezoelectric substrate. It is between about 0.005 and 0.15 with respect to the wavelength [lambda].

Euler angles (12 °, θ, 37 °) of the piezoelectric substrate are plotted on the horizontal axis, and the ratio H / λ of the film thickness H of the interdigital transducer to the wavelength λ excited on the piezoelectric substrate is coordinated on the vertical axis. When denoted by θ and H / λ of the surface acoustic wave, the points described below:

A (θ = 152 °, H / λ = 0.005)

B (θ = 153.5 °, H / λ = 0.005)

C (θ = 155 °, H / λ = 0.15)

D (θ = 153.5 °, H / λ = 0.15)

It is included in the area | region enclosed by or the line surrounding this area | region.

A surface acoustic wave resonator according to various preferred embodiments of the present invention may be provided in a surface acoustic wave filter, a duplexer, or a communication device.

According to a preferred embodiment of the present invention, it is possible to achieve a surface wave resonator having an excellent TCD.

BRIEF DESCRIPTION OF DRAWINGS To illustrate the invention, some preferred examples are shown in the drawings, but are not limited to the precise arrangements and instrumentalities shown in the invention.

EMBODIMENT OF THE INVENTION Hereinafter, embodiment of this invention is described with reference to drawings.

1 is a perspective view of a surface acoustic wave resonator showing a first embodiment of the present invention.

As shown in FIG. 1, the surface acoustic wave resonator 1 forms one IDT on a piezoelectric substrate 2 including La ₃ Ga ₅ SiO ₁₄ single crystals, and forms reflectors 4 on both sides thereof.

The interdigital transducer 3 is preferably formed of an electrode material such as Al or Au, and has a shape in which a pair of comb-shaped electrodes 3a and 3b are interdigitated with each other.

Next, a second embodiment of the present invention will be described. Figure 2 is a perspective view of a longitudinally coupled surface acoustic wave filter showing a second embodiment of the present invention.

As shown in FIG. 2, in the vertically coupled surface acoustic wave filter 11, at least two IDTs 13 and 13 are disposed on a piezoelectric substrate 12 composed of La ₃ Ga ₅ SiO ₁₄ single crystals. Reflectors 14 and 14 are formed on both end surfaces of the IDT.

The IDT 13 is formed of an electrode material such as Al or Au, and the pair of comb-shaped electrodes 13a and 13b are arranged so as to sandwich each other. The IDTs are arranged in parallel at regular intervals in the surface acoustic wave propagation direction.

Moreover, a third embodiment of the present invention will be described. 3 is a perspective view of a horizontally coupled surface acoustic wave filter showing a third preferred embodiment of the present invention.

As shown in FIG. 3, the transverse coupling type surface acoustic wave filter 21 preferably forms an IDT 23 on a piezoelectric substrate 22 composed of La ₃ Ga ₅ SiO ₁₄ single crystals.

The IDT 23 is made of an electrode material such as Al or Au, and the comb-shaped electrodes 23a and 23b are arranged as interdigitated with each other.

A fourth embodiment and a fifth embodiment of the present invention will be described. 4 is a block diagram of a duplexer showing a fourth embodiment of the present invention and a communication device showing a fifth embodiment of the present invention.

As shown in FIG. 4, the communication device 31 includes an antenna 35 connected to an antenna terminal of a duplexer 34 having a receiving surface acoustic wave filter 32 and a transmitting surface acoustic wave filter 33. do. In addition, the communication device 31 includes an output terminal connected to the reception circuit 36 and an input terminal connected to the transmission circuit 37. As the surface acoustic wave filter 32 for reception and the surface acoustic wave filter 33 for transmission of the duplexer 34, the surface acoustic wave filters 11 and 21 described above in the second and third embodiments are used, respectively.

An experiment on the change of temperature and frequency variation was performed by the Euler angle of La ₃ Ga ₅ SiO ₁₄ used as the substrate of the surface acoustic wave device described above. In FIG. 5, actual values of frequency fluctuations affected by temperature are represented by ˜- ◆, and an approximation value is indicated by a curve.

As shown in Fig. 5, it can be seen that in the La ₃ Ga ₅ SiO ₁₄ single crystal, a curve having a peak temperature of a frequency at which the frequency variation becomes almost zero is drawn. In addition, La ₃ Ga ₅ SiO ₁₄ according to the I θ of Euler angles (ψ, θ, φ) of the single crystal grows, it can be seen that this curve moves to the high temperature.

Next, when the θ of the Euler angles ψ, θ, and φ changes, the peak temperature of the frequency at which the frequency variation becomes almost zero was measured. Fig. 6 shows the peak temperature by ■, the approximation of which is represented by a line, and how the peak is changed by varying θ (cut angle at Euler angles (12 °, θ, 37 °) of the oiler angles (ψ, θ, φ)). It indicates whether the temperature changes.

As shown in Fig. 6, as the θ of the Euler angles (ψ, θ, φ) of the La ₃ Ga ₅ SiO ₁₄ single crystal increases, the peak of frequency is similar to the curve shown in Fig. 5 moving toward the high temperature side according to θ. It can be seen that the temperature moves to the high temperature side.

Next, FIG. 7 shows how the curve of the frequency variation with respect to temperature changes with the change in the film thickness H of the Al electrode formed on the piezoelectric substrate of the La ₃ Ga ₅ SiO ₁₄ single crystal.

In Fig. 7, an Al electrode having a film thickness of 1500Å is formed on a piezoelectric substrate composed of La ₃ Ga ₅ SiO ₁₄ single crystals having Euler angles (ψ, θ, φ) of approximately (12 °, 153 °, 37 °), respectively. Is a measured value of 7500, on a piezoelectric substrate composed of La ₃ Ga ₅ SiO ₁₄ single crystals having Euler angles (ψ, θ, φ) of approximately (12 °, 153 °, 37 °), respectively. The measured value at the time of forming an Al electrode is shown. As shown in Fig. 7, it can be seen that as the film thickness H of the Al electrode becomes thicker, the curve moves to the low temperature side.

As described above, as the θ of the Euler angles (ψ, θ, φ) of the La ₃ Ga ₅ SiO ₁₄ single crystal increases, the peak temperature at which the frequency variation becomes almost zero moves to the high temperature side, and the thickness H of the Al electrode becomes thicker. As the temperature increases, the peak temperature moves to the low temperature side.

Since surface acoustic wave devices such as surface acoustic wave resonators and surface acoustic wave filters are used at room temperature, the frequency fluctuation of the surface acoustic wave device can be minimized by setting the peak temperature at which the frequency fluctuation is almost zero between about 20 ° C and 30 ° C. have.

As a result, when the film thickness H of the Al electrode is determined by shifting the peak temperature of the frequency to the high temperature side by the θ value of the Euler angles (ψ, θ, φ) of the La ₃ Ga ₅ SiO ₁₄ single crystal, the peak of the frequency is determined. The temperature can preferably be set between about 20 ° C and 30 ° C.

In the range where the Euler angles (ψ, θ, φ) having the best properties of La ₃ Ga ₅ SiO ₁₄ single crystals are approximately (12 °, 152 ° to 155 °, 37 °), the peak temperature of the frequency is about 20 ° C to The value of the film thickness H of the Al electrode was calculated by experiment so as to be between 30 ° C.

As a result, when Euler angles are approximately (12 °, 152 °, 37 °), the peak temperature of the frequency at H / λ = 0.005 is about 20 ° C, and Euler angles are approximately (12 °, 153.5 °, 37 °). ), It can be seen that the peak temperature of the frequency at H / λ = 0.005 is about 30 ° C.

Moreover, when the Euler angle is approximately (12 °, 153.5 °, 37 °), the peak temperature of the frequency at H / λ = 0.15 is about 20 ° C, and the Euler angle is approximately (12 °, 155 °, 37 °) It was found that the peak temperature of the frequency at H / λ = 0.15 was about 30 ° C.

The area surrounded by the Euler angle and H / λ set in the range where the peak temperature of the frequency is about 20 ° C to 30 ° C is shown in the graph of FIG. 8. That is, the peak temperature of the frequency in the range of about 20 ° C to 30 ° C is defined as point A (oiler angles (12 °, 152 °, 37 °), H / λ = 0.005), point B [oiler angle (12 °, 153.5 °, 37 °), H / λ = 0.005], point C [Euler angle (12 °, 155 °, 37 °), H / λ = 0.15] and point D [Euler angle (12 °, 153.5 °, 37 °), H / λ = 0.15] or on a line surrounding the area, and the frequency variation is smaller than this area or on a line surrounding this area.

Euler angles (ψ, θ, φ) represent the propagation direction of the surface acoustic wave, but an error of 37 ° ± 2 ° occurs in this propagation direction due to an error in the IDT manufacturing process.

In the first to third embodiments of the present invention, the case where Euler angle? Is about 12 ° has been described. However, from now on, it has been found that almost equivalent values can be obtained in the range of 12 ° ± 1 °. . That is, even when ψ is about 11 ° or 13 °, the same effect as that when ψ is 12 ° can be obtained.

In addition, in the first to third embodiments of the present invention, the surface acoustic wave resonator, the longitudinally coupled surface acoustic wave filter, and the transversely coupled surface acoustic wave filter have been described as examples, but are not limited thereto. For example, a horizontal surface acoustic wave filter having a plurality of pairs of transducers and a ladder filter in which the surface acoustic wave resonators are arranged in a ladder circuit shape may be used, and an equivalent effect can be obtained by any type of surface acoustic wave device. .

Further, in the first to third embodiments of the present invention, the surface acoustic wave resonator having a reflector has been described, but is not limited thereto. The present invention is applicable to surface acoustic wave devices without reflectors.

Although a preferred embodiment of the present invention has been disclosed, it is apparent to those skilled in the art that other modifications based on the technical idea of the present invention can be carried out in addition to the embodiments disclosed herein. will be. Therefore, it is understood that the scope of the present invention is not limited to the scope of the following claims.

According to the present invention, the surface acoustic wave device with small frequency variation can be obtained by optimizing the Euler angle of the La ₃ Ga ₅ SiO ₁₄ piezoelectric substrate and the film thickness of the electrode.

Claims (21)

Piezoelectric substrates composed of langasite single crystals; And A surface acoustic wave resonator comprising: an interdigital transducer formed on the piezoelectric substrate. Euler angles (ψ, θ, φ) defining the direction of the piezoelectric substrate are about 11 ° to 13 °, about 152 ° to 155 ° and about 37 ° ± 2 °, respectively. The film thickness H of the interdigital transducer is between 0.005 and 0.15 with respect to the wavelength? Of the surface acoustic wave excited on the piezoelectric substrate. The surface acoustic wave resonator as claimed in claim 1, wherein the interdigital transducer is made of Al. The surface acoustic wave resonator as claimed in claim 1, wherein the interdigital transducer is made of Au. The surface acoustic wave resonator of claim 1, wherein the piezoelectric substrate is made of a La ₃ Ga ₅ SiO ₁₄ single crystal. The surface acoustic wave resonator of claim 1, wherein reflectors are formed on both ends of the piezoelectric substrate. A surface acoustic wave filter having a surface acoustic wave resonator comprising a piezoelectric substrate composed of a langaceite single crystal and an interdigital transducer formed on the piezoelectric substrate, Euler angles (ψ, θ, φ) defining the orientation of the piezoelectric substrate are about 11 ° to 13 °, about 152 ° to 155 ° and about 37 ° ± 2 °, respectively. The film thickness H of the interdigital transducer is between 0.005 and 0.15 with respect to the wavelength? Of the surface acoustic wave excited on the piezoelectric substrate. 7. The surface acoustic wave filter of claim 6, wherein the interdigital transducer is made of Al. The surface acoustic wave filter of claim 6, wherein the interdigital transducer is made of Au. 7. The surface acoustic wave filter as claimed in claim 6, wherein the piezoelectric substrate is composed of La ₃ Ga ₅ SiO ₁₄ single crystals. The surface acoustic wave filter of claim 6, wherein reflectors are formed on both ends of the piezoelectric substrate. A duplexer having a surface acoustic wave device comprising a piezoelectric substrate composed of langagasite single crystal and an interdigital transducer formed on the piezoelectric substrate, Euler angles (ψ, θ, φ) defining the orientation of the piezoelectric substrate are about 11 ° to 13 °, about 152 ° to 155 ° and about 37 ° ± 2 °, respectively. The film thickness H of the interdigital transducer is between 0.005 and 0.15 with respect to the wavelength? Of the surface acoustic wave excited on the piezoelectric substrate. 12. The duplexer according to claim 11, wherein the interdigital transducer is made of Al. 12. The duplexer according to claim 11, wherein the interdigital transducer is made of Au. 12. The duplexer according to claim 11, wherein the piezoelectric substrate is composed of La ₃ Ga ₅ SiO ₁₄ single crystals. The duplexer according to claim 11, wherein reflectors are formed on both ends of the piezoelectric substrate. A communication device having a surface acoustic wave resonator comprising a piezoelectric substrate composed of a langassite single crystal and an interdigital transducer formed on the piezoelectric substrate, Euler angles (ψ, θ, φ) defining the orientation of the piezoelectric substrate are about 11 ° to 13 °, about 152 ° to 155 ° and about 37 ° ± 2 °, respectively. The film thickness H of the interdigital transducer is between 0.005 and 0.15 with respect to the wavelength? Of the surface acoustic wave excited on the piezoelectric substrate. 17. The communications device of claim 16 wherein the interdigital transducer is comprised of Al. 17. The communications device of claim 16 wherein the interdigital transducer is comprised of Au. 17. The communications device of claim 16, wherein said piezoelectric substrate is comprised of La ₃ Ga ₅ SiO ₁₄ single crystals. 17. The communications device of claim 16, wherein reflectors are formed on both ends of the piezoelectric substrate. A piezoelectric substrate composed of rangagasite single crystal; And An interdigital transducer disposed on the piezoelectric substrate, the surface acoustic wave device comprising: Euler angles (12 °, θ, 37 °) of the piezoelectric substrate are plotted on the horizontal axis, and the ratio H / λ of the film thickness H of the interdigital transducer to the wavelength λ excited on the piezoelectric substrate is coordinated on the vertical axis. Represented by (Theta) and H / (lambda) of a surface acoustic wave are contained in the area | region enclosed by the point described below, or on the line surrounding the said area | region, The surface acoustic wave device characterized by the above-mentioned. A (θ = 152 °, H / λ = 0.005) B (θ = 153.5 °, H / λ = 0.005) C (θ = 155 °, H / λ = 0.15) D (θ = 153.5 °, H / λ = 0.15)